Referring to FIG. 1, there is shown in block diagram form a conventional power supply used to provide DC power to portable electronic devices, such as notebook computers, cellular telephones, PDAs, MP3 players and the like. The power supply 2 is capable of receiving an input voltage from a DC power source, such as an automobile or airplane power port, as well as from an AC power source, such as a household wall outlet. Conversion circuitry 4 converts the input voltage to a DC output voltage which may be provided to a first electronic device, such as a notebook PC. The DC voltage provided to the first electronic device may be fixed in the case, for example, that the power supply 2 is dedicated for use with one model of notebook PC. Alternatively, a signal 6 may be used to program the conversion circuitry 4 to provide a particular voltage selectable from a range of output voltages. In this way, the power supply may be used with a variety of electronic devices having differing input voltage requirements. Conversion circuitry and various connector adapters, cables and switches used to program the conversion circuitry are disclosed in U.S. Pat. No. 6,693,413, the disclosure of which is incorporated herein by reference; particular reference is made to FIGS. 7A-7C; 24-40; and 51 of U.S. Pat. No. 6,693,413.
In addition to providing an operating voltage to a first electronic device, the power supply equipment may simultaneously provide an operating voltage to a second electronic device, such as a cellular telephone. A low power regulator 8 receives from the conversion circuitry 4 the voltage being generated for the first electronic device and regulates such voltage to a value used as the input voltage for the second electronic device. Regulator circuitry of this type is shown in FIG. 41 of the aforementioned U.S. Pat. No. 6,693,413. The regulator may be a separate unit from the power supply 2 or it may be housed in the same enclosure as the power supply.
A given power supply has a power rating, i.e., an amount of power (expressed in watts) which the power supply is capable of safely delivering to one or more electronic devices. To prevent a user from coupling to a power supply an electronic device which will draw power in excess of the power rating of the power supply, various connector arrangements were developed. Typically, power is transferred from the power supply to an electronic device via a cable. The far (distal) end of the cable is affixed with a connector. One of several connector adapters may be potentially mated with the cable connector. The connector adapter (also called a tip) serves as an interface between the cable connector and the electronic device. That is, a particular connector adapter is mechanically configured to mate, on one side with a particular electronic device, and on the other side with the cable connector. By use of a resistor within a connector adapter or by other techniques, the connector adapter may serve to program the power supply to produce the specific operational voltage required by the particular electronic device. Based on the programmed operational voltage and the maximum current producible by the power supply, the connector adapter can be said to have a power rating (which should meet or exceed the power requirements of the electronic device).
U.S. Pat. Nos. 6,976,885 and 7,056,149 each discloses cable connector/connector adapter assemblies in which a connector adapter is mechanically prohibited from mating with a cable connector if the power rating of the connector adapter exceeds the power rating of the cable connector, i.e., the power rating of the power supply to which the cable connector is coupled. In addition to a physical keying technique to prohibit mechanical mating of a connector adapter with underrated cable connectors (i.e., power supplies), U.S. Pat. No. 7,056,149 also employs a visual keying technique to discourage the user from attempting such improper mechanical mating in the first place.
Due to improvements in conversion circuitry technology, a power supply which generates power sufficient to run most high power consuming electronic devices, such as notebook computers, can be housed in a reasonably sized casing and provided at an attractive price. In fact, such power supplies can usually supply enough power to simultaneously power a high power consuming electronic device such as a notebook computer, and a low power consuming device, such as a cellular telephone. Powering two low power devices is likewise feasible. However, due to size, heat and cost constraints, it is not desirable to provide a power supply which can provide enough power to simultaneously power two high power devices. Nevertheless, some users will invariably attempt to use the power supply in such a manner.
To prevent a user from connecting a high power device to the low power output (provided by the regulator 8 of FIG. 1, for example), the cable connector/connector adapter assemblies of the prior art could be employed. While sufficient to prohibit the mating of an improper (overrated) connector adapter with a cable connector, such assemblies have drawbacks. For example, some users find such configurations confusing and may become discouraged enough to return the entire product when a connector adapter is not mateable with a connector. Other users will attempt to force an incompatible connector adapter onto a cable connector, thereby damaging the adapter, connector or both.
The same type of problem is encountered even if the power supply is not programmable. For example, a manufacturer may provide various models of notebook computers all of which require 16V as an input voltage and various models of low power devices, such as cellular telephones and MP3 players, all of which require 6V as an input voltage. For such product line, one configuration for a connector at the distal end of the cable can be used for all the notebook computers and such connector can be permanently affixed to the cable (assuming the power input ports of all of the notebooks have the same mechanical configuration as each other). Similarly, one configuration for a connector at the distal end of the cable can be used for all the low power devices and such connector can be permanently affixed to the cable (again assuming the power input ports for all the lower power devices have the same mechanical configuration as each other). To allow the power supply to power acceptable combinations of high power and low power devices, i.e., one high power device, one low power device; and two low power devices, the proximal end of the cables have connectors which detachably mate with connectors serving as the power output ports of the power supply. Based on prior techniques, to prevent the power supply from being used to power an unacceptable combination of devices (i.e., two high power devices), one of the power supply output ports is mechanically configured to accept a low power cable, but not accept a high power cable. Thus, the potential problems of user confusion and damage to the connectors are still present.
Conventionally, if the power supply equipment is configured to allow a user to simultaneously couple two high power devices to the power supply, and the user does so, the power supply will shut down by operation of its overvoltage or overcurrent protection circuitry. That is, based on the load exceeding the power supply power rating, the power supply will interrupt its normal operation and enter a reset mode for a period of time. This not only presents an inconvenience to the user, it places stress on the power supply components. If such stress is repeatedly applied, for example due to the user repeatedly trying to simultaneously power two high power devices, complete failure of the power supply may result.